Multiplex telephony and telegraphy.



UNITED sTATEs PATENT oFFIoE.

GEORGE OWEN SQUIER, 0E THE UNITED STATES ARMY.

MULTIPLEX 1TEI.|EIEIHIOI\TY AND TELEGRAPHY. i

Specication of Letters Patent. Application led Novel-uber 5, 1910. Serial No. 590,802

v1 a1aaa1iea Jan. 3, 1911.

(DEDICATED T0 THE PUBLIC.)

Government of the United States or any of its oliicers or employees in the prosecution of Workfor the United States or by any person in the United States Without the payment of any ,royalty thereon.

This invention relates to multiplex telephony and telegraphy and has as its object the simultaneous transmission of a plurality of telephonic and telegraphic messages over a singlelcircuit.

A further object of the invention is to make use of ,a grounded, or earthed, circuitl for multiplex telephony in such a manner as to avoidthe disturbances arising from such causes as ive trouble in the ordinary grounded telep one circuit.

A further object is to apply electricwaves of such different frequenciesas to make possible the selection and `complete independence of the variousmessages.

A furtherobject is' to superimpose upon a standard battery' telephone circuit, asnow commercially u sed,fone or more telephonie and telegraphic circuits Without any interference of the various messages.

Iii-accomplishing the above results, use is made of electro-magnetic Waves, or oscillations, of high frequency, guided by'wires.

Reference is here made to my co-pending applications. Serial Nos. 590,801 and 590,802, filed November 5, '1910, Iin Which applications I have discussed at length the advantages-and limitations of high frequency electric Waves, or oscillations, for the transmission of intelligence. As in these above `mentioned applications, I ordinarily make use of frequencies above the limit of audibility, which may be taken as ranging 'from about 15,000 cycles per second up, and ac-A cordingly, in this application, when referenceis made to high frequency oscillations, it is understood to mean loscillations ofl u1- tra-sound frequencies or a frequency. above human audition.

, It has been found necessary in order to obtain efficient results to makeus'e of such detectors as are commonly found in the Wire'- less telegraphic art. Attempts have been made at multiplex telephony, but4 I have found these inoperative, for the reason,-

among others, that no detector, or equivalent device, has been used. These detectors are not used because of any greater inherent sensitiveness to electric energy than resides in the telephone receiver itself, but because the energy, being in the form of rapid oscillations, cannot alfect a telephone or other indicating device/ These rapid oscillations cannot sensibly affect the telephone, because the diaphragm in its motion reverses With the reversal of the current, and the deflecting impulse, if applied directly to the telephone receiver, vvill be first in one direction and then in the other, With a frequency `so high that the diaphragm cannot follow or respond. Furthermore, if the diaphragm should respond with this frequency, the effeet Wouldfnot be audible. Also, in the case of the ordinary telephone, on account of the large self-inductance of the instrument, the high frequency E. M. F. generatedvby the Waves would produce in a telephone receiver only extremely Weak currents. Ihave found it necessary, therefore, and consider it anv important part of this invention, to make use of' some form of integrating detector to transform these rapid oscillation into effects which can be manifested by the indicating instruments.

In practice, I have made use of a pair of telephone lilies in the common and ordinary telephone cables, such as is usedlin city telephone traiiic, the pair in use being but one of a large numberof paper-covered twistedpairs inclosed in a lead sheath, the cable being placed principally underground. The electric waves or oscillations pass along this conductor in the manner originally investiwaves along metallic Wires.

The invention described in this applica' tion yis similar to that described in my -scribed includes co-pending applications, Serial Numbers 590,801 and 590,802, filed November 5, 1910, but differs from these in that the high frequency oscillatory circuits are suitably connected to ground or earth. v

In the drawings forming a 'part of this specification, several modifications of the circuit connections are shown, and in said drawings, Figure 1 illustrates a form of circuit in which a highl frequency transmitter and :receiver are connected to the line and to the earth. Fig. 2 shows a modification of this circuit .in which a plurality of high fre-l quency transmitters is used. Fig. 3 shows still anothermodification. y

Referring to these figures in detail, Fig. 1 shows a common metallic circuit for ordinary telephony in which local batteries are used at each station. In this -figure, A and A represent a pair of conductors twisted together and placed within a lead sheath, b eing but one out of a plurality of pairs in sald sheath. Across these line wires are bridged the local telephone sets B and B, each set being precisely similar and comprising a microphone transmitter 1, in series with a battery 2, and the primary of a transformer 3. Thel rlnging circuit is shown `at 4 and the switch hook with its contact points at 5, the receiver at' 6. The telephone set as demerely the ordinary apparatus used in a local telephone set. The invention is not in any way connected with the details of this telephone connection, any other of the usual circuit connections being suitable, and the one described being given merely as an illustration. 'If desired, the choke coils 7 and 8 may be used with the telephone sets as shown, to preventv the passage of high frequency oscillations through l them, but 1n practice I have found this unsufficient impedance in necessary, for the telephone sets interpose themselves to prevent the passage of high frequency currents. Connected t the line at or, .near one of the terminals o vthe telephone set B is a circuit connected to the earth E, this circuit including a variable condenser C, a variable inductance'L, and the secondary- S of the transformer. Inductively connected to the secondaryS is themprimary P of thev transformer, to""which isconnected the 'high fre'- quency generator G, and, in circuit with these, are shown the variable capacity C', theyariable inductance L and the microphone M. At or near the station B is connected a similar circuit containing the variable condenser C1, the variable inductance L1, and the primary P1 of a transformer. the earth connection being shown at E. The secondary S, of the transformer forms part of the oscillatory circuit containing the.

variable capacity C1 and the variable inductance L1. In shunt to the capacity 0, is the detector which may be of any suitable Aform such as the Audion orthe Ferikou.

and L1 serve for the pur- The operation of the device is as follows: l

The high frequency oscillations generated by Gare impresse on the circuit C-L- S, which then travel out on the line A', these oscillations being modified in accordance with -speech by the microphone M. The oscillations are selected and absorbed by the oscillatory circuit C1 L1 S1 which is tuned to the frequency of the oscillations received. These oscillations are then transformed or rectified by the detector D, and the speech is reproduced in ner well understoodin the art of wireless telephony.- The condenser C and the inductance L are used for tuning the generato-r circuit to the frequency of the generator. This is-particularl useful where the power of the generator islimited," but these elements are also useful in regulating the amount of energy supplied by the generator G, for, by throwing the circuits slightly out of tune, the energy transmitted may be materially reduced. An important feature of these connections lies in the condensers C and C1, for these condensers, in addition to serving as tuning elements, isolate the 'line from the earth so far as'ordinary telephonie currents are concerned.

As is well known, it has been 'impossible to obtain satisfactory battery telephony over any circuit which is connected' to ground in any way whatsoever, except in some few cases of elaborate circuits to prevent interference, and then only to a limited extent. Lines constructed with ground circuits are found to be subject to serious diiiiculties, chief among which are the strange noises heard in the receiving instruments.

sufficient effect to make a grounded telephone circuit exceedingly noisy and undesirable. In the present invention. however, I am able to connect a telephone. circuiti toearth at both ends without perceiving the slightest trace of any disturbing noises, and I consider this accomplishment of a silentearth connection the telephone F inthe manand delicate balancing of ',l`he exact eausesyof thesenoises are not entirely understood, but they are of an important feature of my invention. In

actual practice I find that the high frequency telephonie messages and the lo'cal battery telephonie messages may exist on the line simultaneously without "a trace whatsoever of any cross-talk or disturbing noises from other external sources. I consider that this is made possible bythe fact that the condensers O and Ol are of a very small capacity, being measured in terms of thou. sandths of a microfarad and, as such, interpose an extremely high impedance to all cur` rents of such low frequencies as the ordinary telephonie currents or disturbing currents from external sources. Furthermore, since these earth o-r ground connections form la part of tuned circuits including the line, no disturbances from the earth are permitted to pass, since all such earth connections are tuned to frequencies entirely above audition. The result I obtain would be entirely impossible if condensers and inductances of such size as are now commonly used in telephonie practice were inserted in the circuit, yfo-r such condensers and inductances are very large lindeed compared to the ones I actually use.

In some cases, the condenser C on the transmitter end may be omitted, but, in general, results are more satisfactory with both condensers O andC1 in`circuit.

The high frequency oscillation transformers are so constructed as to give a. vari-able coupling in any suitable manner, such, for instance, as sliding the coils S and S, into or out of the primaries P and P, or swinging one Within the other. Obviously any other suitable method for obtaining variable coupling may be used. Y

Fig. 2 shows a form of circuit in Which a plurality of high frequency generators of different frequencies is used to impress energy upon the line circuit A-A. The connection of the local battery sets across the lines is precisely the same as in Fig. 1 and is here shown only diagrammatically at BwB. Connected vat or near the terminal B is a plurality of circuits containinga con-1 denser O, an inductance L, and the second-4 ary of a transformer, connection being made to earth at E. These circuits are precisely the same as were describedin connection With Fig. 1. To each circuit there is inductively connected a transmitter circuit containing a generator With tuning element-s anda suitable signaling instrument. In the circuit T1, I have shown the microphone transmitter replaced by a telegraphic key K, which telegrapliic key may be connected into the circuit in a variety of ways, such, for instance, as shown in this Fig. 2, or as shown in Fig. 3 of my co-pending application, Serial Number 590,801, cited above. At the station B, I have shown a plurality of circuits connected to ground, these circuits containing a. condenser C, and inductance L1, and the vprimary of a. transformer in the manner described in connection with Fig. 1. To each of these circuits, there is inductively connected a receiving circuitsimilar in every respect to lthe "receiver circuit shown and described in connection with Fig.

1. These receivercircuits are tuned to dit'- ferent frequencies, each being tuned to the frequency of one' of the transmitters at the other end of the line. In view of this difference in frequency, it is obvious that osci1 lations sent from the transmitter T will be selected by the receiver R, and oscillations sent by the: transmitter T1 will be selected and received by thereceiver R1, thus giving multiplex telephony or telegraphy by high frequency currents in addition to the ordinar local battery telephone currents. In shunt to the line may be placed condenser-s K and K in order to connect the two lines A and A in parallel for the high frequency currents. These condensers, however, are. of such small dimensions as to interpose a lpractically insuperable impedance to the currents from the` telephone sets B and B. In practice it is not necessary to use the condensers, K and K. Obviously, any number' of high frequency circuits of different periods may be connected to the line circuits, some being connected to the Wire A and some to the Wire A, as shown at R a'nd T. Obviously, also, it will be desirable in practice to have an equal number of receiver and transmitter stations at each end of thelin'e, in order that communication may be carried on in both directions. In this ligure, as in Fig. 1, I have shown a local battery telephone circuit grounded at each end, andl this isv donp Without, in any Way affecting the Working of the local telephone sets, so that I atta-in a silent grounded telephone circuit.

Fig. 3 shows a modification in which one line Wire A and the telephone sets B and B have been entirely eliminated. In this case, a plurality of high frequency transmitters and receivers is i connected to the line` as shown, the transmitters being shown diagrammatically'at T and T and the receivers at R and R. Each of these transmitter and receiver stations is similar to those described in connection with Figs. 1 and 2. There may, ofcourse, be a larger number of these circuits connected lthan is shown, and each transmitter may be tuned to a different frequency and one receiver will be tuned to each transmitter. In this modification, as is grounded Wire, a telephone circuit which is entirely silent so far as disturbing impulses are concerned,'and as I stated previously, l consider this an important feature of my invention. In addition to obtaining a silent grounded one-Wire telephone circuit, I have in this ligure shown multiplex telephony.

InFigs. 1 and 2, I have shown specific forms of transmitter and receiver circuits, but it is obvious that each of these circuits may bemoditied in 4various Ways Without in i any way atfectingmy invention. Modificai tions of these circuits are shown in my col pending application, Serial Number 590,801,

apparent, I have attained with a single orse equipment for a single line with stacircuit drawings for th iforms of circuits shown therein may be suband itis to beunderstood that any of. the earth connections bridged from line to earth,

means for impressing high frequency oscillations of different frequencies on each bridged. connection, means for n iodify stituted for the circuits shown herein.

he standard telegraph circuit of the World employs the earth as the return consuch a standthe regular connections brid from line to earth; a

ard telegraph circuit comprisin end frequency oscillations at each Upon this standard Morse telegraph line are superimposed the tions in each receiver circuit and a telephone high frequency telegraph Acircuits as indioperatively connected -to the detector, each cated in said Fig. 3. I have not shown other pair of corresponding bridge connections with the line wire being tuned to the frequency of the oscillations impressed thereon. standar In a `multiplex telephone and telegraph practiced, yI system, a `pair of line wires, battery teleline, the differential duplex, the polar duphone sets bridged across said line wires' the duplex-diplex, etc., but itis lrnani- I sil fest thatsuch superposition is readily operhigh frequency telegraph vative and practical by the identical methods for generating electric Waves of ultra-sound 85 r and forms of apparatus already fully derequencies connected to one of Said earth scribed in this specification and also in my connections, means for modifying said elecco-pendin applications, Serial Numbers-- tric Waves a receiver circuit connected to 590,802. In general, by shuntingt e present Morse way stationapparatus or ultra-sound electric waves in said reor t e terminal apparatus by a suit-able 10W ceiver circuit and va telephone operatively `valued variable condenser, or condenser and detector.

inductance tuned with the line circuit to the 4 In a multiplex telephone and telegra h high l equency of the generator, the comsystem, a pair of line wires, battery te eplete separatlon 0f the two messages is efphone sets bridged across said ine wires; 95 fected. have n ot, therefore, considered it silent earth connections, including a variable necessaryto multlply drawings in this specicondenser and a variable induotance a d iication to indicate how this is accomplished in each case, but I wish it understood that Waves connected inductively to one of said this invention comprises and includes the ear connections, a telephonetransmitter inet ods as above .described for superlmpOS- for modifying said electric waves; a receiver ing upon' the ,ordinary manual Morse telecircuit connected t ySounders, high to 4another similar earth` ,graph ll'culfs', emPlOylng keys, relays and connection, a detector for high frequency frequency telegraphic oir electric waves in said receiver circuit, and a 4o cuits, 1n the manner and by the means subtelephone operatively connected to the de- 105 Stalltlilll 3S deSCIlbedtector, said receiver circuit and the earth ough several modifications have been connections with the line being tuned to the described in detail in h' apparent that many otherch frequency circuit, a receiver the invention,

- detector.

. wire. low

t 1S SPQCiCafOD, it S frequency of the generator.

5. In a multiplex telephone system, a pair of line wires, battery telephone sets bridged across said line'wires; a plurality of silent earth connections, including variable Acondensers and variable inductances; a pluralanges may be made Withoutdeparting from the spirit of Aand I therefore do not wish to llfe limited to the exact connections shown,

I Ch-mas my nventionis thefolity ofdgenerators of high frequency electric `lovilnti waves of Adifferent ultra-sound frequencies,

1. In a multiplex signaling system a line Wire, low frequency signaling instruments a circuit for equency currents comprising the line and silent earth connections; means for imone connected inductively to each earth con'- nection; microphone transmitters .for each generator for modifying said electric yvaves;

a plurality of earth connect-ions similar to the transmitter earth connections; a `plurality of receiver circuits, one connected to each of the second named earth connections, an integrating detector for high frequency electric waves in each receiver circuit, and a telephone operatively connectedto` the detector;

6. "In a multiplex telephone system, a pair line wires, a condenser of small capacity. ridged across said lines, a plurality of earth connections, including variable condensers 136` fied ing a` detector for electricv waves associated with .said h igh y frequency circuit and a translating device operatively connected to the .2. In a multiplex signaling .system a line frequency signaling instruments connected to said line wire, a plurality of and variable inductances; a plurality of for modifying said electric waves;v a plurality of earth connectlons similar to the transi mitter earth connections; a plurality of receiver circuits, one connected to each of the second named earth connections, an integrating detector for high frequency electric waves in each receiver circuit and a telephone operatively connected to the detector.

T. In a multiplex telephone system, a pair of line wires, battery telephone sets bridged across said line Wiresfa condenser of small capacity connected in parallel to said telephone sets; a plurality of earth connections, including ay Variable condenser and a variable inductance, connected from 'each line wire to earth.; a plurality of transmitter circuits inductively connected to said earth connections,each transmitter circuit including a high frequency generator, a variable capacity, a variable inductance and a microphone transmitter; a plurality of similar earth connections; a `plurality of receiver circuits, one inductively connected to each of the second named earth connections, each receiver circuit including a variable inductance and a variable capacity, a detector shunted around said condenser and a telephone operatively connected to said detector, each receiver circuit and the corresponding pair of bridge circuits with line being tuned to the frequency of its corresponding generator.

GEORGE OVEN SQUIER. Vitnesses:

P. I. `\VoLD, E. R. CRAM. 

